* {
    box-sizing: border-box;
}
.box {
    width: 200px;
    height: 100px;
    padding: 20px;
    border: 5px solid black;
    margin: 10px;
}
.content-box {
    box-sizing: content-box; 
    background-color: lightblue;
}
.border-box {
    box-sizing: border-box; 
    background-color: lightgreen;
}